[NoboruWataya]

Are there that many calendar formats? I thought iCal was by far the most ubiquitous. I've heard of jCal as well but never seen it in the wild.

[jeroenhd]

I'm pretty sure the entire world uses ical files. It's a bit of an annoying format to parse, though. The calendar.txt file format seems to be made for people to interact with it directly through a terminal (which the target audience probably already had open).